This invention relates to a molding apparatus for molding parts having portions that are undercut. In particular, it relates to a mold having coring that is split into three or four sections, which can be moved by a press away from the remainder of the mold and away from each other.
A conventional mold for making an undercut part consists of front and back cavity halves with a coring in between. The coring contains extensions for making the undercuts and is divided into two sections. A hydraulic press closes the cavity halves against the coring and molding compound, placed within the mold either before closing or injected after closing, is cured, usually by heat, to form a solid part. The hydraulic press then pulls the front cavity half away from the back cavity half. Two additional hydraulic cylinders then pull the two sections of the coring apart in a perpendicular direction, thereby freeing the part from the mold; the part is usually dislodged from the mold by hand.
While this type of molding apparatus will successfully produce an undercut part, it requires considerable space due to the long perpendicular distance the two sections must travel in order to free the part, and to the space required for the two hydraulic cylinders. In addition, if a single hydraulic press is to be used for simultaneously molding several parts, to allow room for the hydraulic cylinders, the molds must be assembled in a row and a hydraulic press must be used that is capable of applying the required pressure over the length of the row. This usually means that a larger press is required than would be needed to supply the required pressure because few presses are made that are large enough to handle that distance but are low capacity. For example, a 500 ton press would probably be needed to handle four molds one square foot in area even though a 250 ton press would be adequate for the amount of pressure required. Of course, a larger press adds to the cost of producing the part.